WDMA (computer)
Encyclopedia
The Word DMA interface was the fastest method used to transfer data between the computer (through the ATA controller
) and an ATA device until UDMA
.
Single/Multiword DMA took over from PIO
as the choice of interface between ATA devices and the computer.
The WDMA interface is grouped into different modes.
The explanation for the difference between single and multiword DMA
can be found in how the Intel 8237
DMA chip works.
In single transfer mode only one word (16-bit) will be transferred between the device and the computer before returning control to the CPU and later it will repeat this cycle, allowing the CPU to process data while data is transferred.
In multiword transfer mode (Block mode) once transfer is begun it will continue until all words are transferred.
Two additional Advanced Timing modes have been defined in the CompactFlash
specification 2.1. Those are Multiword DMA mode 3 and Multiword DMA mode 4. They are specific to CompactFlash. Multiword DMA is only permitted for CompactFlash devices configured in True IDE mode.
Controller (computing)
In computing and especially in computer hardware, controller is a chip, an expansion card, or a stand-alone device that interfaces with a peripheral device...
) and an ATA device until UDMA
UDMA
For the main article about the controller, see Parallel ATAThe Ultra DMA interface was the fastest method used to transfer data between the computer and an ATA device until Serial ATA....
.
Single/Multiword DMA took over from PIO
Programmed input/output
Programmed input/output is a method of transferring data between the CPU and a peripheral such as a network adapter or an ATA storage device....
as the choice of interface between ATA devices and the computer.
The WDMA interface is grouped into different modes.
The explanation for the difference between single and multiword DMA
Direct memory access
Direct memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....
can be found in how the Intel 8237
Intel 8237
Intel 8237 is a direct memory access controller , a part of the MCS 85 microprocessor family. It was used as the DMA controller in the original IBM PC and IBM XT...
DMA chip works.
In single transfer mode only one word (16-bit) will be transferred between the device and the computer before returning control to the CPU and later it will repeat this cycle, allowing the CPU to process data while data is transferred.
In multiword transfer mode (Block mode) once transfer is begun it will continue until all words are transferred.
Two additional Advanced Timing modes have been defined in the CompactFlash
CompactFlash
CompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
specification 2.1. Those are Multiword DMA mode 3 and Multiword DMA mode 4. They are specific to CompactFlash. Multiword DMA is only permitted for CompactFlash devices configured in True IDE mode.
| Mode | Max Transfer Rate (MB Megabyte The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000... /s) | Bits | Min cycle time | Defining standard | Single 0 | 2.1 | 16 | 960 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-1 | Single 1 | 4.2 | 16 | 480 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-1 | Single 2 | 8.3 | 16 | 240 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-1 | Multi 0 | 4.2 | 16 | 480 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-1 | Multi 1 | 13.3 | 16 | 150 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-2 | Multi 2 | 16.7 | 16 | 120 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | ATA-2 | Multi 3 | 20 | 16 | 100 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | CompactFlash 2.1 | Multi 4 | 25 | 16 | 80 ns 1 E-9 s A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.... | CompactFlash 2.1 |
|---|
See also
- PIOProgrammed input/outputProgrammed input/output is a method of transferring data between the CPU and a peripheral such as a network adapter or an ATA storage device....
- The first interface type used between devices (mainly hard disks) and the computer. - ATA